1. Field of the Disclosure
The present disclosure relates to a power supply and, more specifically, to stabilizing a power combining power supply system.
2. Description of the Related Art
Many electronic devices tend to require much more sophisticated power supplies for supplying power. For example, many electronics may require high frequency of operation, high overall efficiency, few components, and/or low ripple in the power supplied by the power supplies.
More specifically, there is often a need for a power supply circuit that is capable of delivering power with high frequency components (fast changing voltage and current), at high overall power conversion efficiency. For example, an RF (Radio Frequency) PA (power amplifier) can be fed by an efficient power supply at a reduced voltage, allowing the PA to operate more efficiently (i.e., with lower power consumption). In these RF power amplifiers, the power supply must be capable of changing the output voltage very quickly to accommodate rapid changes in the output power of the PA, requiring the power supply to deliver high frequency components of power. At the same time, a high overall efficiency is desired in the power supply to achieve the desired lower power consumption. A typical switched-mode power supply (SMPS) circuit achieves high efficiency, but cannot deliver sufficiently high frequency components of the power, because the low switching frequencies commonly used in these types of regulators (a limitation largely imposed by the magnetics) limits the regulator's bandwidth. Linear regulators, on the other hand, may be designed to deliver high frequency components, but the power conversion efficiency of such a linear regulator is poor. Thus neither a common SMPS nor a linear regulator can meet this need.
Another example of the need for a power supply that is both efficient and can deliver a fast changing power is one which supplies a digital circuit, which may include a microprocessor. The digital circuit may operate more efficiently if fed by a power supply that adjusts its voltage dynamically to match the predicted processing needs. Typically, the voltage is adjusted upwards when the digital circuit is operating at high speeds, and downward when operating at lower speeds. While conventional power supplies can typically change their voltage within 50 μs, this delay may prevent the digital circuitry from operating at peak efficiency, and a power supply which adjusts its voltage more quickly to allow for a more frequent change in clocking speeds of the digital circuitry is desirable.
There have been some efforts to design power supply circuits that can operate at high frequencies and are also power efficient. One conventional technique uses both a SMPS and a linear regulator to provide power to a load. The linear regulator provides the high frequency power components, and the switching regulator provides the low frequency and DC power components. An inductor and a capacitor are used to combine the outputs from the SMPS and linear regulator to form the output power of the power supply for the load. The configuration of inductor and capacitor causes unwanted ringing that is counteracted by increasing the output impedance of the SMPS and the linear regulator. However, increasing the output impedance of the power supplies has the negative consequence of reducing the efficiency of the power supply circuit.